如何使用图形对象 g 绘制透明形状? [英] How to draw a transparent shape using a Graphics object g?

问题描述

我想在具有透明背景的 BufferedImage 中创建一个环".我可以像这样用透明背景绘制圆圈:

I want to create a "ring" in a BufferedImage with a transparent background. I can draw the circle with a transparent background like this:

BufferedImage bi = new BufferedImage(d, d, BufferedImage.TYPE_INT_ARGB);
Graphics2D g = (Graphics2D) bi.getGraphics();
g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
g.setColor(c);
g.fillOval(0, 0, d, d);

但现在我想在它的中间画一个较小的透明圆圈来制作一个环(所以当我在另一个图像上绘制这个图像时，环周围和内部的像素没有被绘制).我想使用 Graphics 对象来执行此操作，以便我可以使用抗锯齿.

But now I want to draw a smaller transparent circle in the middle of it to make a ring (so when I draw this image over another image, the pixels around and inside the ring are not drawn). I want to use a Graphics object to do this so I can use antialiasing.

这可能吗?如果不是，那么解决这个问题的最佳方法是什么?

Is this possible? If it isn’t, what it the best way to tackle this problem?

推荐答案

创建一个圆形，然后从中减去另一个圆形，将其设置为剪辑 &你最终可能会得到一些符合需要的东西.要隐藏剪辑的粗糙边缘，请绘制一个 2 像素宽的形状笔触.

Create a circular shape, then subtract another circular shape from that, set it as the clip & you might end up with something along the lines needed. To hide the rough edges of the clip, draw a 2px wide stroke of the shape.

import java.awt.*;
import java.awt.geom.*;
import java.awt.image.BufferedImage;
import java.net.URL;
import javax.imageio.ImageIO;
import javax.swing.*;

public class OneRing {

    OneRing(BufferedImage imageBG, BufferedImage imageFG) {
        // presumes the images are identical in size BNI
        int w = imageBG.getWidth();
        int h = imageBG.getHeight();
        Ellipse2D.Double ellipse1 = new Ellipse2D.Double(
                w/16,h/16,7*w/8,7*h/8); 
        Ellipse2D.Double ellipse2 = new Ellipse2D.Double(
                w/4,h/4,w/2,h/2);
        Area circle = new Area(ellipse1);
        circle.subtract(new Area(ellipse2));

        Graphics2D g = imageBG.createGraphics();
        g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g.setRenderingHint(RenderingHints.KEY_DITHERING, RenderingHints.VALUE_DITHER_ENABLE);
        g.setRenderingHint(RenderingHints.KEY_FRACTIONALMETRICS, RenderingHints.VALUE_FRACTIONALMETRICS_ON);
        g.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BICUBIC);
        g.setClip(circle);
        g.drawImage(imageFG, 0, 0, null);
        g.setClip(null);
        Stroke s = new BasicStroke(2);
        g.setStroke(s);
        g.setColor(Color.BLACK);
        g.draw(circle);
        g.dispose();

        JLabel l = new JLabel(new ImageIcon(imageBG));
        JOptionPane.showMessageDialog(null, l);
    }

    public static void main(String[] args) throws Exception {
        URL urlFG = new URL("http://i.stack.imgur.com/OVOg3.jpg");
        URL urlBG = new URL("http://i.stack.imgur.com/lxthA.jpg");
        final BufferedImage biFG = ImageIO.read(urlFG);
        final BufferedImage biBG = ImageIO.read(urlBG);
        SwingUtilities.invokeLater(new Runnable(){
            @Override
            public void run() {
                new OneRing(biBG, biFG);
            }
        });
    }
}

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